The present invention relates to packaging of microelectromechanical (MEM) devices and integrated circuits (ICs), and more particularly to a micromachined structure for attaching one or more die containing a MEM device, an IC or a microsensor to a supporting substrate without the use of an adhesive or solder.
Microelectromechanical (MEM) devices are microminiature devices formed on a substrate using fabrication process steps common to the integrated circuit (IC) fabrication industry. These MEM devices generally combine electrical and mechanical functionality to form many different kinds of electromechanical devices including accelerometers, sensors, motors, switches, relays, coded locks, micromirrors and microfluidic devices.
The fabrication of MEM devices is generally based on the deposition and photolithographic patterning of alternate layers of polycrystalline silicon (also termed polysilicon) and a sacrificial material such as silicon dioxide (SiO2) or a silicate glass (e.g. deposited from the decomposition of tetraethylortho silicate, also termed TEOS). Vias can be etched through the sacrificial material to provide anchor points to the substrate and between adjacent polysilicon layers. The polysilicon layers can be patterned and built up layer by layer to form various members of the MEM device structure. Once the MEM device structure is completed, the sacrificial material is partially or completely removed (e.g. by exposure to a selective etchant which etches away the sacrificial material, but does not chemically attack the polysilicon layers) to release the polysilicon members of the MEM device for operation.
The MEM devices are preferably packaged after release; and in this released state, the MEM devices can be damaged or degraded by exposure to heat, chemicals or moisture. Traditional methods for attaching microelectronics devices in die form to an integrated circuit (IC) package include the use of solders (e.g. eutectic metals), and the use of adhesives (e.g. epoxy). MEM devices can be easily damaged after release by heating to an elevated temperature which is required when using solder for attachment of the MEM devices in die form to a package. As a result, the current practice is to use an epoxy to attach MEM devices in die form to an IC package. However, the evolution of chemicals from the epoxy over time can result in the degradation and/or failure of the sensitive MEM devices. Thus, there is a need for a packaging method for MEM devices that is not based on either the use of elevated temperatures or the use of adhesives in order to improve the reliability of packaged MEM devices over current technology.
An advantage of the present invention is that a mechanical attachment of a MEM device, a microsensor or an IC to a supporting substrate can be performed by micromachining a structure on a surface of the MEM device, microsensor or IC that mechanically interlocks with a complementary structure formed on a mating surface of the supporting substrate so that the attachment can be made without the use of any solder or adhesive.
Another advantage of the present invention is that a detachable attachment can be formed between the MEM device, microsensor or IC and the supporting substrate.
A further advantage is that one or more electrical interconnections can be made between the MEM device, microsensor or IC and the supporting substrate by electrically conducting portions of a micromachined die attachment structure formed according to the present invention.
Still another advantage of the present invention is that an alignment structure can be provided on the MEM device, microsensor or IC and the supporting substrate to aid in bringing the devices into precise alignment with the supporting substrate to facilitate attachment thereto.
These and other advantages of the method of the present invention will become evident to those skilled in the art.
The present invention relates to a micromechanical structure for attaching a pair of substrates together, with at least one of:the substrates comprising a semiconductor. The attachment structure comprises a first plurality of shaped pillars of a substantially uniform width extending outward from and supported by a first surface of a first substrate of the pair of a substrates; and engagement means formed on a second surface of a second substrate of the pair of substrates for engaging with the outward-extending pillars and forming a mechanical attachment thereto when the first and second surfaces are urged together. The first substrate can be, for example, a semiconductor substrate (e.g. comprising silicon) whereon the MEM device, microsensor or IC is formed; and the second substrate can be the supporting substrate.
Each pillar of the first plurality of shaped pillars can be solid or hollow, and can have a cross-sectional shape in a plane parallel to the first surface that is arbitrarily shaped, and can be, for example, circular, elliptical or polygonal (e.g. square, rectangular, or hexagonal). Each pillar of the first plurality of shaped pillars can further comprise one or more materials selected from the group consisting of monocrystalline silicon, polycrystalline silicon, silicon nitride, silicon dioxide, silicate glasses, polyimide, metals and metal alloys. Additionally, each pillar of the first plurality of shaped pillars can be tapered at an unsupported end thereof and/or slotted along a portion of its length. Furthermore, a sidewall of each pillar of the first plurality of shaped pillars can be roughened or can include one or more ridges or notches formed thereabout to provide a stronger mechanical attachment between the MEM device, microsensor or IC and the supporting substrate. Finally, at least a portion of the first plurality of shaped pillars can be made electrically conductive to provide electrical interconnections between the MEM device, microsensor or IC and the supporting substrate.
The engagement means formed on the second surface of the second substrate (e.g. the supporting substrate) can comprise a second plurality of shaped pillars, with the second plurality of shaped pillars extending outward from and being supported by the second surface of the second substrate. Each pillar formed on the second substrate can be either substantially equal in size and shape to the pillars formed on the first substrate; or in the alternative, each pillar formed on the second substrate can be unequal in size and/or shape to the pillars formed on the first substrate. Each pillar formed on the second substrate can also be solid or hollow, can have a substantially uniform width, can be tapered at an unsupported end thereof, or can be slotted along a portion of its length. Each pillar formed on the second substrate can be adapted to fit adjacent to or around or within one of the pillars on the first substrate. To strengthen the interlocking or attachment between the first and second substrates, the pillars on one substrate can include one or more notches formed therearound; and the mating pillars on the other substrate can include one or more ridges formed therearound.
The attachment structure of the present invention can further include an optional alignment structure formed on the first and second substrates to aid in precisely positioning the first plurality of shaped pillars with the engagement means, thereby facilitating formation of the mechanical attachment therebetween. The alignment structure can comprise, for example, a plurality of shaped pegs formed on one of the first and second substrates, and a plurality of shaped recesses for receiving the shaped pegs formed on the other of the first and second substrates. The shaped pegs are larger in size than the shaped pillars and can be tapered at an unsupported end thereof, with the tapered end being substantially flat rather than pointed. The shaped recesses can have either substantially vertical sidewalls or sidewalls that are tapered inward at an angle with increasing depth. Each shaped peg can further have a length that exceeds the length of the pillars so that the shaped pegs come into contact with the mating substrate before the pillars are engaged. This helps to ensure that the attachment structure can be easily and simply positioned to bring the shaped pillars into position for subsequent engagement.
In other embodiments of the present invention, the engagement means can comprise a deformable layer formed above the second surface of the second substrate, with the deformable layer having a plurality of openings therethrough superposed with the first plurality of shaped pillars. In these embodiments of the present invention, the first plurality of shaped pillars can be as described previously, and optionally can be tapered at an unsupported end thereof, or optionally can include one or more ridges or notches formed about an outer sidewall thereof.
In yet other embodiments of the present invention, the engagement means can comprise an array of receptacles formed on the second substrate, with each receptacle further comprising a cavity that is adapted to receive a mating pillar of the first plurality of shaped pillars. Each receptacle can comprise a cavity having a width substantially equal to the width of the mating pillar, with each mating pillar being either solid or hollow and optionally being slotted along a portion of its length. Additionally, each receptacle optionally can include a notch or ridge formed about an inner sidewall of the cavity, with the mating pillar having a complementary ridge or notch formed about an outer sidewall thereof.
The present invention also relates to a structure for attaching at least one semiconductor die (e.g. comprising silicon) to a supporting substrate, with the attachment structure comprising a plurality of downward-extending pillars having a substantially uniform width formed on a lower surface of each semiconductor die in a spaced arrangement, and further comprising a plurality of upward-extending pillars formed on an upper surface of the supporting substrate. The upward-extending pillars are spaced for engagement with the downward-extending pillars to provide a mechanical attachment of each semiconductor die to the supporting substrate upon urging the die and substrate together. Each semiconductor die can further include a device such as microelectromechanical (MEM) device, an integrated circuit (IC) device or a microsensor device formed on or below a surface thereof (e.g. in a region of the semiconductor die that is free from the plurality of the downward-extending pillars).
The present invention is further related to a structure for attaching a pair of substrates together with at least one of the substrates being a semiconductor. The attachment structure can comprise a plurality of shaped pillars of a substantially uniform width extending downward from a first substrate of the pair of substrates; and a plurality of sockets or receptacles formed on or below a surface of a second substrate of the pair of substrates, with each socket or receptacle being adapted to receive and engage one of the pillars, thereby attaching the pair of substrates together. An alignment structure can optionally be provided for bringing the pair of substrates into precise alignment with each other. Such an alignment structure can comprise, for example, a plurality of shaped recesses formed into one of the pair of substrates and a plurality of shaped pegs formed in the other of the pair of substrates, with each shaped recess and each shaped peg having substantially equal lateral dimensions at one end thereof and substantially different lateral dimensions at the other end thereof (i.e. a mating end of each of the shaped recesses and shaped pegs can be tapered, the opposite end being untapered with substantially vertical sidewalls).
Additional advantages and novel features of the invention will become apparent to those skilled in the art upon examination of the following detailed description thereof when considered in conjunction with the accompanying drawings. The advantages of the invention can be realized and attained by means of the instrumentalities and combinations particularly:pointed out in the appended claims.